1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * mm/userfaultfd.c
4 *
5 * Copyright (C) 2015 Red Hat, Inc.
6 */
7
8 #include <linux/mm.h>
9 #include <linux/sched/signal.h>
10 #include <linux/pagemap.h>
11 #include <linux/rmap.h>
12 #include <linux/swap.h>
13 #include <linux/swapops.h>
14 #include <linux/userfaultfd_k.h>
15 #include <linux/mmu_notifier.h>
16 #include <linux/hugetlb.h>
17 #include <linux/shmem_fs.h>
18 #include <asm/tlbflush.h>
19 #include <asm/tlb.h>
20 #include "internal.h"
21 #include "swap.h"
22
23 static __always_inline
validate_dst_vma(struct vm_area_struct * dst_vma,unsigned long dst_end)24 bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
25 {
26 /* Make sure that the dst range is fully within dst_vma. */
27 if (dst_end > dst_vma->vm_end)
28 return false;
29
30 /*
31 * Check the vma is registered in uffd, this is required to
32 * enforce the VM_MAYWRITE check done at uffd registration
33 * time.
34 */
35 if (!dst_vma->vm_userfaultfd_ctx.ctx)
36 return false;
37
38 return true;
39 }
40
41 static __always_inline
find_vma_and_prepare_anon(struct mm_struct * mm,unsigned long addr)42 struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
43 unsigned long addr)
44 {
45 struct vm_area_struct *vma;
46
47 mmap_assert_locked(mm);
48 vma = vma_lookup(mm, addr);
49 if (!vma)
50 vma = ERR_PTR(-ENOENT);
51 else if (!(vma->vm_flags & VM_SHARED) &&
52 unlikely(anon_vma_prepare(vma)))
53 vma = ERR_PTR(-ENOMEM);
54
55 return vma;
56 }
57
58 #ifdef CONFIG_PER_VMA_LOCK
59 /*
60 * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
61 * @mm: mm to search vma in.
62 * @address: address that the vma should contain.
63 *
64 * Should be called without holding mmap_lock.
65 *
66 * Return: A locked vma containing @address, -ENOENT if no vma is found, or
67 * -ENOMEM if anon_vma couldn't be allocated.
68 */
uffd_lock_vma(struct mm_struct * mm,unsigned long address)69 static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
70 unsigned long address)
71 {
72 struct vm_area_struct *vma;
73
74 vma = lock_vma_under_rcu(mm, address);
75 if (vma) {
76 /*
77 * We know we're going to need to use anon_vma, so check
78 * that early.
79 */
80 if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
81 vma_end_read(vma);
82 else
83 return vma;
84 }
85
86 mmap_read_lock(mm);
87 vma = find_vma_and_prepare_anon(mm, address);
88 if (!IS_ERR(vma)) {
89 bool locked = vma_start_read_locked(vma);
90
91 if (!locked)
92 vma = ERR_PTR(-EAGAIN);
93 }
94
95 mmap_read_unlock(mm);
96 return vma;
97 }
98
uffd_mfill_lock(struct mm_struct * dst_mm,unsigned long dst_start,unsigned long len)99 static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
100 unsigned long dst_start,
101 unsigned long len)
102 {
103 struct vm_area_struct *dst_vma;
104
105 dst_vma = uffd_lock_vma(dst_mm, dst_start);
106 if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
107 return dst_vma;
108
109 vma_end_read(dst_vma);
110 return ERR_PTR(-ENOENT);
111 }
112
uffd_mfill_unlock(struct vm_area_struct * vma)113 static void uffd_mfill_unlock(struct vm_area_struct *vma)
114 {
115 vma_end_read(vma);
116 }
117
118 #else
119
uffd_mfill_lock(struct mm_struct * dst_mm,unsigned long dst_start,unsigned long len)120 static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
121 unsigned long dst_start,
122 unsigned long len)
123 {
124 struct vm_area_struct *dst_vma;
125
126 mmap_read_lock(dst_mm);
127 dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
128 if (IS_ERR(dst_vma))
129 goto out_unlock;
130
131 if (validate_dst_vma(dst_vma, dst_start + len))
132 return dst_vma;
133
134 dst_vma = ERR_PTR(-ENOENT);
135 out_unlock:
136 mmap_read_unlock(dst_mm);
137 return dst_vma;
138 }
139
uffd_mfill_unlock(struct vm_area_struct * vma)140 static void uffd_mfill_unlock(struct vm_area_struct *vma)
141 {
142 mmap_read_unlock(vma->vm_mm);
143 }
144 #endif
145
146 /* Check if dst_addr is outside of file's size. Must be called with ptl held. */
mfill_file_over_size(struct vm_area_struct * dst_vma,unsigned long dst_addr)147 static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
148 unsigned long dst_addr)
149 {
150 struct inode *inode;
151 pgoff_t offset, max_off;
152
153 if (!dst_vma->vm_file)
154 return false;
155
156 inode = dst_vma->vm_file->f_inode;
157 offset = linear_page_index(dst_vma, dst_addr);
158 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
159 return offset >= max_off;
160 }
161
162 /*
163 * Install PTEs, to map dst_addr (within dst_vma) to page.
164 *
165 * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
166 * and anon, and for both shared and private VMAs.
167 */
mfill_atomic_install_pte(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,struct page * page,bool newly_allocated,uffd_flags_t flags)168 int mfill_atomic_install_pte(pmd_t *dst_pmd,
169 struct vm_area_struct *dst_vma,
170 unsigned long dst_addr, struct page *page,
171 bool newly_allocated, uffd_flags_t flags)
172 {
173 int ret;
174 struct mm_struct *dst_mm = dst_vma->vm_mm;
175 pte_t _dst_pte, *dst_pte;
176 bool writable = dst_vma->vm_flags & VM_WRITE;
177 bool vm_shared = dst_vma->vm_flags & VM_SHARED;
178 spinlock_t *ptl;
179 struct folio *folio = page_folio(page);
180 bool page_in_cache = folio_mapping(folio);
181
182 _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
183 _dst_pte = pte_mkdirty(_dst_pte);
184 if (page_in_cache && !vm_shared)
185 writable = false;
186 if (writable)
187 _dst_pte = pte_mkwrite(_dst_pte, dst_vma);
188 if (flags & MFILL_ATOMIC_WP)
189 _dst_pte = pte_mkuffd_wp(_dst_pte);
190
191 ret = -EAGAIN;
192 dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
193 if (!dst_pte)
194 goto out;
195
196 if (mfill_file_over_size(dst_vma, dst_addr)) {
197 ret = -EFAULT;
198 goto out_unlock;
199 }
200
201 ret = -EEXIST;
202 /*
203 * We allow to overwrite a pte marker: consider when both MISSING|WP
204 * registered, we firstly wr-protect a none pte which has no page cache
205 * page backing it, then access the page.
206 */
207 if (!pte_none_mostly(ptep_get(dst_pte)))
208 goto out_unlock;
209
210 if (page_in_cache) {
211 /* Usually, cache pages are already added to LRU */
212 if (newly_allocated)
213 folio_add_lru(folio);
214 folio_add_file_rmap_pte(folio, page, dst_vma);
215 } else {
216 folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE);
217 folio_add_lru_vma(folio, dst_vma);
218 }
219
220 /*
221 * Must happen after rmap, as mm_counter() checks mapping (via
222 * PageAnon()), which is set by __page_set_anon_rmap().
223 */
224 inc_mm_counter(dst_mm, mm_counter(folio));
225
226 set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
227
228 /* No need to invalidate - it was non-present before */
229 update_mmu_cache(dst_vma, dst_addr, dst_pte);
230 ret = 0;
231 out_unlock:
232 pte_unmap_unlock(dst_pte, ptl);
233 out:
234 return ret;
235 }
236
mfill_atomic_pte_copy(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,unsigned long src_addr,uffd_flags_t flags,struct folio ** foliop)237 static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
238 struct vm_area_struct *dst_vma,
239 unsigned long dst_addr,
240 unsigned long src_addr,
241 uffd_flags_t flags,
242 struct folio **foliop)
243 {
244 void *kaddr;
245 int ret;
246 struct folio *folio;
247
248 if (!*foliop) {
249 ret = -ENOMEM;
250 folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma,
251 dst_addr);
252 if (!folio)
253 goto out;
254
255 kaddr = kmap_local_folio(folio, 0);
256 /*
257 * The read mmap_lock is held here. Despite the
258 * mmap_lock being read recursive a deadlock is still
259 * possible if a writer has taken a lock. For example:
260 *
261 * process A thread 1 takes read lock on own mmap_lock
262 * process A thread 2 calls mmap, blocks taking write lock
263 * process B thread 1 takes page fault, read lock on own mmap lock
264 * process B thread 2 calls mmap, blocks taking write lock
265 * process A thread 1 blocks taking read lock on process B
266 * process B thread 1 blocks taking read lock on process A
267 *
268 * Disable page faults to prevent potential deadlock
269 * and retry the copy outside the mmap_lock.
270 */
271 pagefault_disable();
272 ret = copy_from_user(kaddr, (const void __user *) src_addr,
273 PAGE_SIZE);
274 pagefault_enable();
275 kunmap_local(kaddr);
276
277 /* fallback to copy_from_user outside mmap_lock */
278 if (unlikely(ret)) {
279 ret = -ENOENT;
280 *foliop = folio;
281 /* don't free the page */
282 goto out;
283 }
284
285 flush_dcache_folio(folio);
286 } else {
287 folio = *foliop;
288 *foliop = NULL;
289 }
290
291 /*
292 * The memory barrier inside __folio_mark_uptodate makes sure that
293 * preceding stores to the page contents become visible before
294 * the set_pte_at() write.
295 */
296 __folio_mark_uptodate(folio);
297
298 ret = -ENOMEM;
299 if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
300 goto out_release;
301
302 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
303 &folio->page, true, flags);
304 if (ret)
305 goto out_release;
306 out:
307 return ret;
308 out_release:
309 folio_put(folio);
310 goto out;
311 }
312
mfill_atomic_pte_zeroed_folio(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr)313 static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
314 struct vm_area_struct *dst_vma,
315 unsigned long dst_addr)
316 {
317 struct folio *folio;
318 int ret = -ENOMEM;
319
320 folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
321 if (!folio)
322 return ret;
323
324 if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
325 goto out_put;
326
327 /*
328 * The memory barrier inside __folio_mark_uptodate makes sure that
329 * zeroing out the folio become visible before mapping the page
330 * using set_pte_at(). See do_anonymous_page().
331 */
332 __folio_mark_uptodate(folio);
333
334 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
335 &folio->page, true, 0);
336 if (ret)
337 goto out_put;
338
339 return 0;
340 out_put:
341 folio_put(folio);
342 return ret;
343 }
344
mfill_atomic_pte_zeropage(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr)345 static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
346 struct vm_area_struct *dst_vma,
347 unsigned long dst_addr)
348 {
349 pte_t _dst_pte, *dst_pte;
350 spinlock_t *ptl;
351 int ret;
352
353 if (mm_forbids_zeropage(dst_vma->vm_mm))
354 return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
355
356 _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
357 dst_vma->vm_page_prot));
358 ret = -EAGAIN;
359 dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
360 if (!dst_pte)
361 goto out;
362 if (mfill_file_over_size(dst_vma, dst_addr)) {
363 ret = -EFAULT;
364 goto out_unlock;
365 }
366 ret = -EEXIST;
367 if (!pte_none(ptep_get(dst_pte)))
368 goto out_unlock;
369 set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
370 /* No need to invalidate - it was non-present before */
371 update_mmu_cache(dst_vma, dst_addr, dst_pte);
372 ret = 0;
373 out_unlock:
374 pte_unmap_unlock(dst_pte, ptl);
375 out:
376 return ret;
377 }
378
379 /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
mfill_atomic_pte_continue(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,uffd_flags_t flags)380 static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
381 struct vm_area_struct *dst_vma,
382 unsigned long dst_addr,
383 uffd_flags_t flags)
384 {
385 struct inode *inode = file_inode(dst_vma->vm_file);
386 pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
387 struct folio *folio;
388 struct page *page;
389 int ret;
390
391 ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
392 /* Our caller expects us to return -EFAULT if we failed to find folio */
393 if (ret == -ENOENT)
394 ret = -EFAULT;
395 if (ret)
396 goto out;
397 if (!folio) {
398 ret = -EFAULT;
399 goto out;
400 }
401
402 page = folio_file_page(folio, pgoff);
403 if (PageHWPoison(page)) {
404 ret = -EIO;
405 goto out_release;
406 }
407
408 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
409 page, false, flags);
410 if (ret)
411 goto out_release;
412
413 folio_unlock(folio);
414 ret = 0;
415 out:
416 return ret;
417 out_release:
418 folio_unlock(folio);
419 folio_put(folio);
420 goto out;
421 }
422
423 /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
mfill_atomic_pte_poison(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,uffd_flags_t flags)424 static int mfill_atomic_pte_poison(pmd_t *dst_pmd,
425 struct vm_area_struct *dst_vma,
426 unsigned long dst_addr,
427 uffd_flags_t flags)
428 {
429 int ret;
430 struct mm_struct *dst_mm = dst_vma->vm_mm;
431 pte_t _dst_pte, *dst_pte;
432 spinlock_t *ptl;
433
434 _dst_pte = make_pte_marker(PTE_MARKER_POISONED);
435 ret = -EAGAIN;
436 dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
437 if (!dst_pte)
438 goto out;
439
440 if (mfill_file_over_size(dst_vma, dst_addr)) {
441 ret = -EFAULT;
442 goto out_unlock;
443 }
444
445 ret = -EEXIST;
446 /* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */
447 if (!pte_none(ptep_get(dst_pte)))
448 goto out_unlock;
449
450 set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
451
452 /* No need to invalidate - it was non-present before */
453 update_mmu_cache(dst_vma, dst_addr, dst_pte);
454 ret = 0;
455 out_unlock:
456 pte_unmap_unlock(dst_pte, ptl);
457 out:
458 return ret;
459 }
460
mm_alloc_pmd(struct mm_struct * mm,unsigned long address)461 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
462 {
463 pgd_t *pgd;
464 p4d_t *p4d;
465 pud_t *pud;
466
467 pgd = pgd_offset(mm, address);
468 p4d = p4d_alloc(mm, pgd, address);
469 if (!p4d)
470 return NULL;
471 pud = pud_alloc(mm, p4d, address);
472 if (!pud)
473 return NULL;
474 /*
475 * Note that we didn't run this because the pmd was
476 * missing, the *pmd may be already established and in
477 * turn it may also be a trans_huge_pmd.
478 */
479 return pmd_alloc(mm, pud, address);
480 }
481
482 #ifdef CONFIG_HUGETLB_PAGE
483 /*
484 * mfill_atomic processing for HUGETLB vmas. Note that this routine is
485 * called with either vma-lock or mmap_lock held, it will release the lock
486 * before returning.
487 */
mfill_atomic_hugetlb(struct userfaultfd_ctx * ctx,struct vm_area_struct * dst_vma,unsigned long dst_start,unsigned long src_start,unsigned long len,uffd_flags_t flags)488 static __always_inline ssize_t mfill_atomic_hugetlb(
489 struct userfaultfd_ctx *ctx,
490 struct vm_area_struct *dst_vma,
491 unsigned long dst_start,
492 unsigned long src_start,
493 unsigned long len,
494 uffd_flags_t flags)
495 {
496 struct mm_struct *dst_mm = dst_vma->vm_mm;
497 ssize_t err;
498 pte_t *dst_pte;
499 unsigned long src_addr, dst_addr;
500 long copied;
501 struct folio *folio;
502 unsigned long vma_hpagesize;
503 pgoff_t idx;
504 u32 hash;
505 struct address_space *mapping;
506
507 /*
508 * There is no default zero huge page for all huge page sizes as
509 * supported by hugetlb. A PMD_SIZE huge pages may exist as used
510 * by THP. Since we can not reliably insert a zero page, this
511 * feature is not supported.
512 */
513 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
514 up_read(&ctx->map_changing_lock);
515 uffd_mfill_unlock(dst_vma);
516 return -EINVAL;
517 }
518
519 src_addr = src_start;
520 dst_addr = dst_start;
521 copied = 0;
522 folio = NULL;
523 vma_hpagesize = vma_kernel_pagesize(dst_vma);
524
525 /*
526 * Validate alignment based on huge page size
527 */
528 err = -EINVAL;
529 if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
530 goto out_unlock;
531
532 retry:
533 /*
534 * On routine entry dst_vma is set. If we had to drop mmap_lock and
535 * retry, dst_vma will be set to NULL and we must lookup again.
536 */
537 if (!dst_vma) {
538 dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
539 if (IS_ERR(dst_vma)) {
540 err = PTR_ERR(dst_vma);
541 goto out;
542 }
543
544 err = -ENOENT;
545 if (!is_vm_hugetlb_page(dst_vma))
546 goto out_unlock_vma;
547
548 err = -EINVAL;
549 if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
550 goto out_unlock_vma;
551
552 /*
553 * If memory mappings are changing because of non-cooperative
554 * operation (e.g. mremap) running in parallel, bail out and
555 * request the user to retry later
556 */
557 down_read(&ctx->map_changing_lock);
558 err = -EAGAIN;
559 if (atomic_read(&ctx->mmap_changing))
560 goto out_unlock;
561 }
562
563 while (src_addr < src_start + len) {
564 VM_WARN_ON_ONCE(dst_addr >= dst_start + len);
565
566 /*
567 * Serialize via vma_lock and hugetlb_fault_mutex.
568 * vma_lock ensures the dst_pte remains valid even
569 * in the case of shared pmds. fault mutex prevents
570 * races with other faulting threads.
571 */
572 idx = linear_page_index(dst_vma, dst_addr);
573 mapping = dst_vma->vm_file->f_mapping;
574 hash = hugetlb_fault_mutex_hash(mapping, idx);
575 mutex_lock(&hugetlb_fault_mutex_table[hash]);
576 hugetlb_vma_lock_read(dst_vma);
577
578 err = -ENOMEM;
579 dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
580 if (!dst_pte) {
581 hugetlb_vma_unlock_read(dst_vma);
582 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
583 goto out_unlock;
584 }
585
586 if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
587 !huge_pte_none_mostly(huge_ptep_get(dst_mm, dst_addr, dst_pte))) {
588 err = -EEXIST;
589 hugetlb_vma_unlock_read(dst_vma);
590 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
591 goto out_unlock;
592 }
593
594 err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr,
595 src_addr, flags, &folio);
596
597 hugetlb_vma_unlock_read(dst_vma);
598 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
599
600 cond_resched();
601
602 if (unlikely(err == -ENOENT)) {
603 up_read(&ctx->map_changing_lock);
604 uffd_mfill_unlock(dst_vma);
605 VM_WARN_ON_ONCE(!folio);
606
607 err = copy_folio_from_user(folio,
608 (const void __user *)src_addr, true);
609 if (unlikely(err)) {
610 err = -EFAULT;
611 goto out;
612 }
613
614 dst_vma = NULL;
615 goto retry;
616 } else
617 VM_WARN_ON_ONCE(folio);
618
619 if (!err) {
620 dst_addr += vma_hpagesize;
621 src_addr += vma_hpagesize;
622 copied += vma_hpagesize;
623
624 if (fatal_signal_pending(current))
625 err = -EINTR;
626 }
627 if (err)
628 break;
629 }
630
631 out_unlock:
632 up_read(&ctx->map_changing_lock);
633 out_unlock_vma:
634 uffd_mfill_unlock(dst_vma);
635 out:
636 if (folio)
637 folio_put(folio);
638 VM_WARN_ON_ONCE(copied < 0);
639 VM_WARN_ON_ONCE(err > 0);
640 VM_WARN_ON_ONCE(!copied && !err);
641 return copied ? copied : err;
642 }
643 #else /* !CONFIG_HUGETLB_PAGE */
644 /* fail at build time if gcc attempts to use this */
645 extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
646 struct vm_area_struct *dst_vma,
647 unsigned long dst_start,
648 unsigned long src_start,
649 unsigned long len,
650 uffd_flags_t flags);
651 #endif /* CONFIG_HUGETLB_PAGE */
652
mfill_atomic_pte(pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,unsigned long src_addr,uffd_flags_t flags,struct folio ** foliop)653 static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
654 struct vm_area_struct *dst_vma,
655 unsigned long dst_addr,
656 unsigned long src_addr,
657 uffd_flags_t flags,
658 struct folio **foliop)
659 {
660 ssize_t err;
661
662 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) {
663 return mfill_atomic_pte_continue(dst_pmd, dst_vma,
664 dst_addr, flags);
665 } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
666 return mfill_atomic_pte_poison(dst_pmd, dst_vma,
667 dst_addr, flags);
668 }
669
670 /*
671 * The normal page fault path for a shmem will invoke the
672 * fault, fill the hole in the file and COW it right away. The
673 * result generates plain anonymous memory. So when we are
674 * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
675 * generate anonymous memory directly without actually filling
676 * the hole. For the MAP_PRIVATE case the robustness check
677 * only happens in the pagetable (to verify it's still none)
678 * and not in the radix tree.
679 */
680 if (!(dst_vma->vm_flags & VM_SHARED)) {
681 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY))
682 err = mfill_atomic_pte_copy(dst_pmd, dst_vma,
683 dst_addr, src_addr,
684 flags, foliop);
685 else
686 err = mfill_atomic_pte_zeropage(dst_pmd,
687 dst_vma, dst_addr);
688 } else {
689 err = shmem_mfill_atomic_pte(dst_pmd, dst_vma,
690 dst_addr, src_addr,
691 flags, foliop);
692 }
693
694 return err;
695 }
696
mfill_atomic(struct userfaultfd_ctx * ctx,unsigned long dst_start,unsigned long src_start,unsigned long len,uffd_flags_t flags)697 static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
698 unsigned long dst_start,
699 unsigned long src_start,
700 unsigned long len,
701 uffd_flags_t flags)
702 {
703 struct mm_struct *dst_mm = ctx->mm;
704 struct vm_area_struct *dst_vma;
705 ssize_t err;
706 pmd_t *dst_pmd;
707 unsigned long src_addr, dst_addr;
708 long copied;
709 struct folio *folio;
710
711 /*
712 * Sanitize the command parameters:
713 */
714 VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
715 VM_WARN_ON_ONCE(len & ~PAGE_MASK);
716
717 /* Does the address range wrap, or is the span zero-sized? */
718 VM_WARN_ON_ONCE(src_start + len <= src_start);
719 VM_WARN_ON_ONCE(dst_start + len <= dst_start);
720
721 src_addr = src_start;
722 dst_addr = dst_start;
723 copied = 0;
724 folio = NULL;
725 retry:
726 /*
727 * Make sure the vma is not shared, that the dst range is
728 * both valid and fully within a single existing vma.
729 */
730 dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
731 if (IS_ERR(dst_vma)) {
732 err = PTR_ERR(dst_vma);
733 goto out;
734 }
735
736 /*
737 * If memory mappings are changing because of non-cooperative
738 * operation (e.g. mremap) running in parallel, bail out and
739 * request the user to retry later
740 */
741 down_read(&ctx->map_changing_lock);
742 err = -EAGAIN;
743 if (atomic_read(&ctx->mmap_changing))
744 goto out_unlock;
745
746 err = -EINVAL;
747 /*
748 * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
749 * it will overwrite vm_ops, so vma_is_anonymous must return false.
750 */
751 if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
752 dst_vma->vm_flags & VM_SHARED))
753 goto out_unlock;
754
755 /*
756 * validate 'mode' now that we know the dst_vma: don't allow
757 * a wrprotect copy if the userfaultfd didn't register as WP.
758 */
759 if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP))
760 goto out_unlock;
761
762 /*
763 * If this is a HUGETLB vma, pass off to appropriate routine
764 */
765 if (is_vm_hugetlb_page(dst_vma))
766 return mfill_atomic_hugetlb(ctx, dst_vma, dst_start,
767 src_start, len, flags);
768
769 if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
770 goto out_unlock;
771 if (!vma_is_shmem(dst_vma) &&
772 uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
773 goto out_unlock;
774
775 while (src_addr < src_start + len) {
776 pmd_t dst_pmdval;
777
778 VM_WARN_ON_ONCE(dst_addr >= dst_start + len);
779
780 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
781 if (unlikely(!dst_pmd)) {
782 err = -ENOMEM;
783 break;
784 }
785
786 dst_pmdval = pmdp_get_lockless(dst_pmd);
787 if (unlikely(pmd_none(dst_pmdval)) &&
788 unlikely(__pte_alloc(dst_mm, dst_pmd))) {
789 err = -ENOMEM;
790 break;
791 }
792 dst_pmdval = pmdp_get_lockless(dst_pmd);
793 /*
794 * If the dst_pmd is THP don't override it and just be strict.
795 * (This includes the case where the PMD used to be THP and
796 * changed back to none after __pte_alloc().)
797 */
798 if (unlikely(!pmd_present(dst_pmdval) ||
799 pmd_trans_huge(dst_pmdval))) {
800 err = -EEXIST;
801 break;
802 }
803 if (unlikely(pmd_bad(dst_pmdval))) {
804 err = -EFAULT;
805 break;
806 }
807 /*
808 * For shmem mappings, khugepaged is allowed to remove page
809 * tables under us; pte_offset_map_lock() will deal with that.
810 */
811
812 err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr,
813 src_addr, flags, &folio);
814 cond_resched();
815
816 if (unlikely(err == -ENOENT)) {
817 void *kaddr;
818
819 up_read(&ctx->map_changing_lock);
820 uffd_mfill_unlock(dst_vma);
821 VM_WARN_ON_ONCE(!folio);
822
823 kaddr = kmap_local_folio(folio, 0);
824 err = copy_from_user(kaddr,
825 (const void __user *) src_addr,
826 PAGE_SIZE);
827 kunmap_local(kaddr);
828 if (unlikely(err)) {
829 err = -EFAULT;
830 goto out;
831 }
832 flush_dcache_folio(folio);
833 goto retry;
834 } else
835 VM_WARN_ON_ONCE(folio);
836
837 if (!err) {
838 dst_addr += PAGE_SIZE;
839 src_addr += PAGE_SIZE;
840 copied += PAGE_SIZE;
841
842 if (fatal_signal_pending(current))
843 err = -EINTR;
844 }
845 if (err)
846 break;
847 }
848
849 out_unlock:
850 up_read(&ctx->map_changing_lock);
851 uffd_mfill_unlock(dst_vma);
852 out:
853 if (folio)
854 folio_put(folio);
855 VM_WARN_ON_ONCE(copied < 0);
856 VM_WARN_ON_ONCE(err > 0);
857 VM_WARN_ON_ONCE(!copied && !err);
858 return copied ? copied : err;
859 }
860
mfill_atomic_copy(struct userfaultfd_ctx * ctx,unsigned long dst_start,unsigned long src_start,unsigned long len,uffd_flags_t flags)861 ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
862 unsigned long src_start, unsigned long len,
863 uffd_flags_t flags)
864 {
865 return mfill_atomic(ctx, dst_start, src_start, len,
866 uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
867 }
868
mfill_atomic_zeropage(struct userfaultfd_ctx * ctx,unsigned long start,unsigned long len)869 ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
870 unsigned long start,
871 unsigned long len)
872 {
873 return mfill_atomic(ctx, start, 0, len,
874 uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
875 }
876
mfill_atomic_continue(struct userfaultfd_ctx * ctx,unsigned long start,unsigned long len,uffd_flags_t flags)877 ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
878 unsigned long len, uffd_flags_t flags)
879 {
880
881 /*
882 * A caller might reasonably assume that UFFDIO_CONTINUE contains an
883 * smp_wmb() to ensure that any writes to the about-to-be-mapped page by
884 * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to
885 * subsequent loads from the page through the newly mapped address range.
886 */
887 smp_wmb();
888
889 return mfill_atomic(ctx, start, 0, len,
890 uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
891 }
892
mfill_atomic_poison(struct userfaultfd_ctx * ctx,unsigned long start,unsigned long len,uffd_flags_t flags)893 ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
894 unsigned long len, uffd_flags_t flags)
895 {
896 return mfill_atomic(ctx, start, 0, len,
897 uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
898 }
899
uffd_wp_range(struct vm_area_struct * dst_vma,unsigned long start,unsigned long len,bool enable_wp)900 long uffd_wp_range(struct vm_area_struct *dst_vma,
901 unsigned long start, unsigned long len, bool enable_wp)
902 {
903 unsigned int mm_cp_flags;
904 struct mmu_gather tlb;
905 long ret;
906
907 VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end,
908 "The address range exceeds VMA boundary.\n");
909 if (enable_wp)
910 mm_cp_flags = MM_CP_UFFD_WP;
911 else
912 mm_cp_flags = MM_CP_UFFD_WP_RESOLVE;
913
914 /*
915 * vma->vm_page_prot already reflects that uffd-wp is enabled for this
916 * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed
917 * to be write-protected as default whenever protection changes.
918 * Try upgrading write permissions manually.
919 */
920 if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))
921 mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
922 tlb_gather_mmu(&tlb, dst_vma->vm_mm);
923 ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);
924 tlb_finish_mmu(&tlb);
925
926 return ret;
927 }
928
mwriteprotect_range(struct userfaultfd_ctx * ctx,unsigned long start,unsigned long len,bool enable_wp)929 int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
930 unsigned long len, bool enable_wp)
931 {
932 struct mm_struct *dst_mm = ctx->mm;
933 unsigned long end = start + len;
934 unsigned long _start, _end;
935 struct vm_area_struct *dst_vma;
936 unsigned long page_mask;
937 long err;
938 VMA_ITERATOR(vmi, dst_mm, start);
939
940 /*
941 * Sanitize the command parameters:
942 */
943 VM_WARN_ON_ONCE(start & ~PAGE_MASK);
944 VM_WARN_ON_ONCE(len & ~PAGE_MASK);
945
946 /* Does the address range wrap, or is the span zero-sized? */
947 VM_WARN_ON_ONCE(start + len <= start);
948
949 mmap_read_lock(dst_mm);
950
951 /*
952 * If memory mappings are changing because of non-cooperative
953 * operation (e.g. mremap) running in parallel, bail out and
954 * request the user to retry later
955 */
956 down_read(&ctx->map_changing_lock);
957 err = -EAGAIN;
958 if (atomic_read(&ctx->mmap_changing))
959 goto out_unlock;
960
961 err = -ENOENT;
962 for_each_vma_range(vmi, dst_vma, end) {
963
964 if (!userfaultfd_wp(dst_vma)) {
965 err = -ENOENT;
966 break;
967 }
968
969 if (is_vm_hugetlb_page(dst_vma)) {
970 err = -EINVAL;
971 page_mask = vma_kernel_pagesize(dst_vma) - 1;
972 if ((start & page_mask) || (len & page_mask))
973 break;
974 }
975
976 _start = max(dst_vma->vm_start, start);
977 _end = min(dst_vma->vm_end, end);
978
979 err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp);
980
981 /* Return 0 on success, <0 on failures */
982 if (err < 0)
983 break;
984 err = 0;
985 }
986 out_unlock:
987 up_read(&ctx->map_changing_lock);
988 mmap_read_unlock(dst_mm);
989 return err;
990 }
991
992
double_pt_lock(spinlock_t * ptl1,spinlock_t * ptl2)993 void double_pt_lock(spinlock_t *ptl1,
994 spinlock_t *ptl2)
995 __acquires(ptl1)
996 __acquires(ptl2)
997 {
998 if (ptl1 > ptl2)
999 swap(ptl1, ptl2);
1000 /* lock in virtual address order to avoid lock inversion */
1001 spin_lock(ptl1);
1002 if (ptl1 != ptl2)
1003 spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING);
1004 else
1005 __acquire(ptl2);
1006 }
1007
double_pt_unlock(spinlock_t * ptl1,spinlock_t * ptl2)1008 void double_pt_unlock(spinlock_t *ptl1,
1009 spinlock_t *ptl2)
1010 __releases(ptl1)
1011 __releases(ptl2)
1012 {
1013 spin_unlock(ptl1);
1014 if (ptl1 != ptl2)
1015 spin_unlock(ptl2);
1016 else
1017 __release(ptl2);
1018 }
1019
is_pte_pages_stable(pte_t * dst_pte,pte_t * src_pte,pte_t orig_dst_pte,pte_t orig_src_pte,pmd_t * dst_pmd,pmd_t dst_pmdval)1020 static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte,
1021 pte_t orig_dst_pte, pte_t orig_src_pte,
1022 pmd_t *dst_pmd, pmd_t dst_pmdval)
1023 {
1024 return pte_same(ptep_get(src_pte), orig_src_pte) &&
1025 pte_same(ptep_get(dst_pte), orig_dst_pte) &&
1026 pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd));
1027 }
1028
1029 /*
1030 * Checks if the two ptes and the corresponding folio are eligible for batched
1031 * move. If so, then returns pointer to the locked folio. Otherwise, returns NULL.
1032 *
1033 * NOTE: folio's reference is not required as the whole operation is within
1034 * PTL's critical section.
1035 */
check_ptes_for_batched_move(struct vm_area_struct * src_vma,unsigned long src_addr,pte_t * src_pte,pte_t * dst_pte,struct anon_vma * src_anon_vma)1036 static struct folio *check_ptes_for_batched_move(struct vm_area_struct *src_vma,
1037 unsigned long src_addr,
1038 pte_t *src_pte, pte_t *dst_pte,
1039 struct anon_vma *src_anon_vma)
1040 {
1041 pte_t orig_dst_pte, orig_src_pte;
1042 struct folio *folio;
1043
1044 orig_dst_pte = ptep_get(dst_pte);
1045 if (!pte_none(orig_dst_pte))
1046 return NULL;
1047
1048 orig_src_pte = ptep_get(src_pte);
1049 if (!pte_present(orig_src_pte) || is_zero_pfn(pte_pfn(orig_src_pte)))
1050 return NULL;
1051
1052 folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
1053 if (!folio || !folio_trylock(folio))
1054 return NULL;
1055 if (!PageAnonExclusive(&folio->page) || folio_test_large(folio) ||
1056 folio_anon_vma(folio) != src_anon_vma) {
1057 folio_unlock(folio);
1058 return NULL;
1059 }
1060 return folio;
1061 }
1062
1063 /*
1064 * Moves src folios to dst in a batch as long as they share the same
1065 * anon_vma as the first folio, are not large, and can successfully
1066 * take the lock via folio_trylock().
1067 */
move_present_ptes(struct mm_struct * mm,struct vm_area_struct * dst_vma,struct vm_area_struct * src_vma,unsigned long dst_addr,unsigned long src_addr,pte_t * dst_pte,pte_t * src_pte,pte_t orig_dst_pte,pte_t orig_src_pte,pmd_t * dst_pmd,pmd_t dst_pmdval,spinlock_t * dst_ptl,spinlock_t * src_ptl,struct folio ** first_src_folio,unsigned long len,struct anon_vma * src_anon_vma)1068 static long move_present_ptes(struct mm_struct *mm,
1069 struct vm_area_struct *dst_vma,
1070 struct vm_area_struct *src_vma,
1071 unsigned long dst_addr, unsigned long src_addr,
1072 pte_t *dst_pte, pte_t *src_pte,
1073 pte_t orig_dst_pte, pte_t orig_src_pte,
1074 pmd_t *dst_pmd, pmd_t dst_pmdval,
1075 spinlock_t *dst_ptl, spinlock_t *src_ptl,
1076 struct folio **first_src_folio, unsigned long len,
1077 struct anon_vma *src_anon_vma)
1078 {
1079 int err = 0;
1080 struct folio *src_folio = *first_src_folio;
1081 unsigned long src_start = src_addr;
1082 unsigned long src_end;
1083
1084 len = pmd_addr_end(dst_addr, dst_addr + len) - dst_addr;
1085 src_end = pmd_addr_end(src_addr, src_addr + len);
1086 flush_cache_range(src_vma, src_addr, src_end);
1087 double_pt_lock(dst_ptl, src_ptl);
1088
1089 if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
1090 dst_pmd, dst_pmdval)) {
1091 err = -EAGAIN;
1092 goto out;
1093 }
1094 if (folio_test_large(src_folio) ||
1095 folio_maybe_dma_pinned(src_folio) ||
1096 !PageAnonExclusive(&src_folio->page)) {
1097 err = -EBUSY;
1098 goto out;
1099 }
1100 /* It's safe to drop the reference now as the page-table is holding one. */
1101 folio_put(*first_src_folio);
1102 *first_src_folio = NULL;
1103 arch_enter_lazy_mmu_mode();
1104
1105 while (true) {
1106 orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
1107 /* Folio got pinned from under us. Put it back and fail the move. */
1108 if (folio_maybe_dma_pinned(src_folio)) {
1109 set_pte_at(mm, src_addr, src_pte, orig_src_pte);
1110 err = -EBUSY;
1111 break;
1112 }
1113
1114 folio_move_anon_rmap(src_folio, dst_vma);
1115 src_folio->index = linear_page_index(dst_vma, dst_addr);
1116
1117 orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
1118 /* Set soft dirty bit so userspace can notice the pte was moved */
1119 #ifdef CONFIG_MEM_SOFT_DIRTY
1120 orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
1121 #endif
1122 if (pte_dirty(orig_src_pte))
1123 orig_dst_pte = pte_mkdirty(orig_dst_pte);
1124 orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);
1125 set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);
1126
1127 src_addr += PAGE_SIZE;
1128 if (src_addr == src_end)
1129 break;
1130 dst_addr += PAGE_SIZE;
1131 dst_pte++;
1132 src_pte++;
1133
1134 folio_unlock(src_folio);
1135 src_folio = check_ptes_for_batched_move(src_vma, src_addr, src_pte,
1136 dst_pte, src_anon_vma);
1137 if (!src_folio)
1138 break;
1139 }
1140
1141 arch_leave_lazy_mmu_mode();
1142 if (src_addr > src_start)
1143 flush_tlb_range(src_vma, src_start, src_addr);
1144
1145 if (src_folio)
1146 folio_unlock(src_folio);
1147 out:
1148 double_pt_unlock(dst_ptl, src_ptl);
1149 return src_addr > src_start ? src_addr - src_start : err;
1150 }
1151
move_swap_pte(struct mm_struct * mm,struct vm_area_struct * dst_vma,unsigned long dst_addr,unsigned long src_addr,pte_t * dst_pte,pte_t * src_pte,pte_t orig_dst_pte,pte_t orig_src_pte,pmd_t * dst_pmd,pmd_t dst_pmdval,spinlock_t * dst_ptl,spinlock_t * src_ptl,struct folio * src_folio,struct swap_info_struct * si,swp_entry_t entry)1152 static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
1153 unsigned long dst_addr, unsigned long src_addr,
1154 pte_t *dst_pte, pte_t *src_pte,
1155 pte_t orig_dst_pte, pte_t orig_src_pte,
1156 pmd_t *dst_pmd, pmd_t dst_pmdval,
1157 spinlock_t *dst_ptl, spinlock_t *src_ptl,
1158 struct folio *src_folio,
1159 struct swap_info_struct *si, swp_entry_t entry)
1160 {
1161 /*
1162 * Check if the folio still belongs to the target swap entry after
1163 * acquiring the lock. Folio can be freed in the swap cache while
1164 * not locked.
1165 */
1166 if (src_folio && unlikely(!folio_test_swapcache(src_folio) ||
1167 entry.val != src_folio->swap.val))
1168 return -EAGAIN;
1169
1170 double_pt_lock(dst_ptl, src_ptl);
1171
1172 if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
1173 dst_pmd, dst_pmdval)) {
1174 double_pt_unlock(dst_ptl, src_ptl);
1175 return -EAGAIN;
1176 }
1177
1178 /*
1179 * The src_folio resides in the swapcache, requiring an update to its
1180 * index and mapping to align with the dst_vma, where a swap-in may
1181 * occur and hit the swapcache after moving the PTE.
1182 */
1183 if (src_folio) {
1184 folio_move_anon_rmap(src_folio, dst_vma);
1185 src_folio->index = linear_page_index(dst_vma, dst_addr);
1186 } else {
1187 /*
1188 * Check if the swap entry is cached after acquiring the src_pte
1189 * lock. Otherwise, we might miss a newly loaded swap cache folio.
1190 *
1191 * Check swap_map directly to minimize overhead, READ_ONCE is sufficient.
1192 * We are trying to catch newly added swap cache, the only possible case is
1193 * when a folio is swapped in and out again staying in swap cache, using the
1194 * same entry before the PTE check above. The PTL is acquired and released
1195 * twice, each time after updating the swap_map's flag. So holding
1196 * the PTL here ensures we see the updated value. False positive is possible,
1197 * e.g. SWP_SYNCHRONOUS_IO swapin may set the flag without touching the
1198 * cache, or during the tiny synchronization window between swap cache and
1199 * swap_map, but it will be gone very quickly, worst result is retry jitters.
1200 */
1201 if (READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE) {
1202 double_pt_unlock(dst_ptl, src_ptl);
1203 return -EAGAIN;
1204 }
1205 }
1206
1207 orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
1208 #ifdef CONFIG_MEM_SOFT_DIRTY
1209 orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
1210 #endif
1211 set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
1212 double_pt_unlock(dst_ptl, src_ptl);
1213
1214 return PAGE_SIZE;
1215 }
1216
move_zeropage_pte(struct mm_struct * mm,struct vm_area_struct * dst_vma,struct vm_area_struct * src_vma,unsigned long dst_addr,unsigned long src_addr,pte_t * dst_pte,pte_t * src_pte,pte_t orig_dst_pte,pte_t orig_src_pte,pmd_t * dst_pmd,pmd_t dst_pmdval,spinlock_t * dst_ptl,spinlock_t * src_ptl)1217 static int move_zeropage_pte(struct mm_struct *mm,
1218 struct vm_area_struct *dst_vma,
1219 struct vm_area_struct *src_vma,
1220 unsigned long dst_addr, unsigned long src_addr,
1221 pte_t *dst_pte, pte_t *src_pte,
1222 pte_t orig_dst_pte, pte_t orig_src_pte,
1223 pmd_t *dst_pmd, pmd_t dst_pmdval,
1224 spinlock_t *dst_ptl, spinlock_t *src_ptl)
1225 {
1226 pte_t zero_pte;
1227
1228 double_pt_lock(dst_ptl, src_ptl);
1229 if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
1230 dst_pmd, dst_pmdval)) {
1231 double_pt_unlock(dst_ptl, src_ptl);
1232 return -EAGAIN;
1233 }
1234
1235 zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
1236 dst_vma->vm_page_prot));
1237 ptep_clear_flush(src_vma, src_addr, src_pte);
1238 set_pte_at(mm, dst_addr, dst_pte, zero_pte);
1239 double_pt_unlock(dst_ptl, src_ptl);
1240
1241 return PAGE_SIZE;
1242 }
1243
1244
1245 /*
1246 * The mmap_lock for reading is held by the caller. Just move the page(s)
1247 * from src_pmd to dst_pmd if possible, and return number of bytes moved.
1248 * On failure, an error code is returned.
1249 */
move_pages_ptes(struct mm_struct * mm,pmd_t * dst_pmd,pmd_t * src_pmd,struct vm_area_struct * dst_vma,struct vm_area_struct * src_vma,unsigned long dst_addr,unsigned long src_addr,unsigned long len,__u64 mode)1250 static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
1251 struct vm_area_struct *dst_vma,
1252 struct vm_area_struct *src_vma,
1253 unsigned long dst_addr, unsigned long src_addr,
1254 unsigned long len, __u64 mode)
1255 {
1256 swp_entry_t entry;
1257 struct swap_info_struct *si = NULL;
1258 pte_t orig_src_pte, orig_dst_pte;
1259 pte_t src_folio_pte;
1260 spinlock_t *src_ptl, *dst_ptl;
1261 pte_t *src_pte = NULL;
1262 pte_t *dst_pte = NULL;
1263 pmd_t dummy_pmdval;
1264 pmd_t dst_pmdval;
1265 struct folio *src_folio = NULL;
1266 struct anon_vma *src_anon_vma = NULL;
1267 struct mmu_notifier_range range;
1268 long ret = 0;
1269
1270 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1271 src_addr, src_addr + len);
1272 mmu_notifier_invalidate_range_start(&range);
1273 retry:
1274 /*
1275 * Use the maywrite version to indicate that dst_pte will be modified,
1276 * since dst_pte needs to be none, the subsequent pte_same() check
1277 * cannot prevent the dst_pte page from being freed concurrently, so we
1278 * also need to abtain dst_pmdval and recheck pmd_same() later.
1279 */
1280 dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dst_pmdval,
1281 &dst_ptl);
1282
1283 /* Retry if a huge pmd materialized from under us */
1284 if (unlikely(!dst_pte)) {
1285 ret = -EAGAIN;
1286 goto out;
1287 }
1288
1289 /*
1290 * Unlike dst_pte, the subsequent pte_same() check can ensure the
1291 * stability of the src_pte page, so there is no need to get pmdval,
1292 * just pass a dummy variable to it.
1293 */
1294 src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval,
1295 &src_ptl);
1296
1297 /*
1298 * We held the mmap_lock for reading so MADV_DONTNEED
1299 * can zap transparent huge pages under us, or the
1300 * transparent huge page fault can establish new
1301 * transparent huge pages under us.
1302 */
1303 if (unlikely(!src_pte)) {
1304 ret = -EAGAIN;
1305 goto out;
1306 }
1307
1308 /* Sanity checks before the operation */
1309 if (pmd_none(*dst_pmd) || pmd_none(*src_pmd) ||
1310 pmd_trans_huge(*dst_pmd) || pmd_trans_huge(*src_pmd)) {
1311 ret = -EINVAL;
1312 goto out;
1313 }
1314
1315 spin_lock(dst_ptl);
1316 orig_dst_pte = ptep_get(dst_pte);
1317 spin_unlock(dst_ptl);
1318 if (!pte_none(orig_dst_pte)) {
1319 ret = -EEXIST;
1320 goto out;
1321 }
1322
1323 spin_lock(src_ptl);
1324 orig_src_pte = ptep_get(src_pte);
1325 spin_unlock(src_ptl);
1326 if (pte_none(orig_src_pte)) {
1327 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES))
1328 ret = -ENOENT;
1329 else /* nothing to do to move a hole */
1330 ret = PAGE_SIZE;
1331 goto out;
1332 }
1333
1334 /* If PTE changed after we locked the folio them start over */
1335 if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) {
1336 ret = -EAGAIN;
1337 goto out;
1338 }
1339
1340 if (pte_present(orig_src_pte)) {
1341 if (is_zero_pfn(pte_pfn(orig_src_pte))) {
1342 ret = move_zeropage_pte(mm, dst_vma, src_vma,
1343 dst_addr, src_addr, dst_pte, src_pte,
1344 orig_dst_pte, orig_src_pte,
1345 dst_pmd, dst_pmdval, dst_ptl, src_ptl);
1346 goto out;
1347 }
1348
1349 /*
1350 * Pin and lock both source folio and anon_vma. Since we are in
1351 * RCU read section, we can't block, so on contention have to
1352 * unmap the ptes, obtain the lock and retry.
1353 */
1354 if (!src_folio) {
1355 struct folio *folio;
1356 bool locked;
1357
1358 /*
1359 * Pin the page while holding the lock to be sure the
1360 * page isn't freed under us
1361 */
1362 spin_lock(src_ptl);
1363 if (!pte_same(orig_src_pte, ptep_get(src_pte))) {
1364 spin_unlock(src_ptl);
1365 ret = -EAGAIN;
1366 goto out;
1367 }
1368
1369 folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
1370 if (!folio || !PageAnonExclusive(&folio->page)) {
1371 spin_unlock(src_ptl);
1372 ret = -EBUSY;
1373 goto out;
1374 }
1375
1376 locked = folio_trylock(folio);
1377 /*
1378 * We avoid waiting for folio lock with a raised
1379 * refcount for large folios because extra refcounts
1380 * will result in split_folio() failing later and
1381 * retrying. If multiple tasks are trying to move a
1382 * large folio we can end up livelocking.
1383 */
1384 if (!locked && folio_test_large(folio)) {
1385 spin_unlock(src_ptl);
1386 ret = -EAGAIN;
1387 goto out;
1388 }
1389
1390 folio_get(folio);
1391 src_folio = folio;
1392 src_folio_pte = orig_src_pte;
1393 spin_unlock(src_ptl);
1394
1395 if (!locked) {
1396 pte_unmap(src_pte);
1397 pte_unmap(dst_pte);
1398 src_pte = dst_pte = NULL;
1399 /* now we can block and wait */
1400 folio_lock(src_folio);
1401 goto retry;
1402 }
1403
1404 if (WARN_ON_ONCE(!folio_test_anon(src_folio))) {
1405 ret = -EBUSY;
1406 goto out;
1407 }
1408 }
1409
1410 /* at this point we have src_folio locked */
1411 if (folio_test_large(src_folio)) {
1412 /* split_folio() can block */
1413 pte_unmap(src_pte);
1414 pte_unmap(dst_pte);
1415 src_pte = dst_pte = NULL;
1416 ret = split_folio(src_folio);
1417 if (ret)
1418 goto out;
1419 /* have to reacquire the folio after it got split */
1420 folio_unlock(src_folio);
1421 folio_put(src_folio);
1422 src_folio = NULL;
1423 goto retry;
1424 }
1425
1426 if (!src_anon_vma) {
1427 /*
1428 * folio_referenced walks the anon_vma chain
1429 * without the folio lock. Serialize against it with
1430 * the anon_vma lock, the folio lock is not enough.
1431 */
1432 src_anon_vma = folio_get_anon_vma(src_folio);
1433 if (!src_anon_vma) {
1434 /* page was unmapped from under us */
1435 ret = -EAGAIN;
1436 goto out;
1437 }
1438 if (!anon_vma_trylock_write(src_anon_vma)) {
1439 pte_unmap(src_pte);
1440 pte_unmap(dst_pte);
1441 src_pte = dst_pte = NULL;
1442 /* now we can block and wait */
1443 anon_vma_lock_write(src_anon_vma);
1444 goto retry;
1445 }
1446 }
1447
1448 ret = move_present_ptes(mm, dst_vma, src_vma,
1449 dst_addr, src_addr, dst_pte, src_pte,
1450 orig_dst_pte, orig_src_pte, dst_pmd,
1451 dst_pmdval, dst_ptl, src_ptl, &src_folio,
1452 len, src_anon_vma);
1453 } else {
1454 struct folio *folio = NULL;
1455
1456 entry = pte_to_swp_entry(orig_src_pte);
1457 if (non_swap_entry(entry)) {
1458 if (is_migration_entry(entry)) {
1459 pte_unmap(src_pte);
1460 pte_unmap(dst_pte);
1461 src_pte = dst_pte = NULL;
1462 migration_entry_wait(mm, src_pmd, src_addr);
1463 ret = -EAGAIN;
1464 } else
1465 ret = -EFAULT;
1466 goto out;
1467 }
1468
1469 if (!pte_swp_exclusive(orig_src_pte)) {
1470 ret = -EBUSY;
1471 goto out;
1472 }
1473
1474 si = get_swap_device(entry);
1475 if (unlikely(!si)) {
1476 ret = -EAGAIN;
1477 goto out;
1478 }
1479 /*
1480 * Verify the existence of the swapcache. If present, the folio's
1481 * index and mapping must be updated even when the PTE is a swap
1482 * entry. The anon_vma lock is not taken during this process since
1483 * the folio has already been unmapped, and the swap entry is
1484 * exclusive, preventing rmap walks.
1485 *
1486 * For large folios, return -EBUSY immediately, as split_folio()
1487 * also returns -EBUSY when attempting to split unmapped large
1488 * folios in the swapcache. This issue needs to be resolved
1489 * separately to allow proper handling.
1490 */
1491 if (!src_folio)
1492 folio = swap_cache_get_folio(entry);
1493 if (folio) {
1494 if (folio_test_large(folio)) {
1495 ret = -EBUSY;
1496 folio_put(folio);
1497 goto out;
1498 }
1499 src_folio = folio;
1500 src_folio_pte = orig_src_pte;
1501 if (!folio_trylock(src_folio)) {
1502 pte_unmap(src_pte);
1503 pte_unmap(dst_pte);
1504 src_pte = dst_pte = NULL;
1505 put_swap_device(si);
1506 si = NULL;
1507 /* now we can block and wait */
1508 folio_lock(src_folio);
1509 goto retry;
1510 }
1511 }
1512 ret = move_swap_pte(mm, dst_vma, dst_addr, src_addr, dst_pte, src_pte,
1513 orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval,
1514 dst_ptl, src_ptl, src_folio, si, entry);
1515 }
1516
1517 out:
1518 if (src_anon_vma) {
1519 anon_vma_unlock_write(src_anon_vma);
1520 put_anon_vma(src_anon_vma);
1521 }
1522 if (src_folio) {
1523 folio_unlock(src_folio);
1524 folio_put(src_folio);
1525 }
1526 /*
1527 * Unmap in reverse order (LIFO) to maintain proper kmap_local
1528 * index ordering when CONFIG_HIGHPTE is enabled. We mapped dst_pte
1529 * first, then src_pte, so we must unmap src_pte first, then dst_pte.
1530 */
1531 if (src_pte)
1532 pte_unmap(src_pte);
1533 if (dst_pte)
1534 pte_unmap(dst_pte);
1535 mmu_notifier_invalidate_range_end(&range);
1536 if (si)
1537 put_swap_device(si);
1538
1539 return ret;
1540 }
1541
1542 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
move_splits_huge_pmd(unsigned long dst_addr,unsigned long src_addr,unsigned long src_end)1543 static inline bool move_splits_huge_pmd(unsigned long dst_addr,
1544 unsigned long src_addr,
1545 unsigned long src_end)
1546 {
1547 return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) ||
1548 src_end - src_addr < HPAGE_PMD_SIZE;
1549 }
1550 #else
move_splits_huge_pmd(unsigned long dst_addr,unsigned long src_addr,unsigned long src_end)1551 static inline bool move_splits_huge_pmd(unsigned long dst_addr,
1552 unsigned long src_addr,
1553 unsigned long src_end)
1554 {
1555 /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */
1556 return false;
1557 }
1558 #endif
1559
vma_move_compatible(struct vm_area_struct * vma)1560 static inline bool vma_move_compatible(struct vm_area_struct *vma)
1561 {
1562 return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB |
1563 VM_MIXEDMAP | VM_SHADOW_STACK));
1564 }
1565
validate_move_areas(struct userfaultfd_ctx * ctx,struct vm_area_struct * src_vma,struct vm_area_struct * dst_vma)1566 static int validate_move_areas(struct userfaultfd_ctx *ctx,
1567 struct vm_area_struct *src_vma,
1568 struct vm_area_struct *dst_vma)
1569 {
1570 /* Only allow moving if both have the same access and protection */
1571 if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) ||
1572 pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot))
1573 return -EINVAL;
1574
1575 /* Only allow moving if both are mlocked or both aren't */
1576 if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED))
1577 return -EINVAL;
1578
1579 /*
1580 * For now, we keep it simple and only move between writable VMAs.
1581 * Access flags are equal, therefore cheching only the source is enough.
1582 */
1583 if (!(src_vma->vm_flags & VM_WRITE))
1584 return -EINVAL;
1585
1586 /* Check if vma flags indicate content which can be moved */
1587 if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma))
1588 return -EINVAL;
1589
1590 /* Ensure dst_vma is registered in uffd we are operating on */
1591 if (!dst_vma->vm_userfaultfd_ctx.ctx ||
1592 dst_vma->vm_userfaultfd_ctx.ctx != ctx)
1593 return -EINVAL;
1594
1595 /* Only allow moving across anonymous vmas */
1596 if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
1597 return -EINVAL;
1598
1599 return 0;
1600 }
1601
1602 static __always_inline
find_vmas_mm_locked(struct mm_struct * mm,unsigned long dst_start,unsigned long src_start,struct vm_area_struct ** dst_vmap,struct vm_area_struct ** src_vmap)1603 int find_vmas_mm_locked(struct mm_struct *mm,
1604 unsigned long dst_start,
1605 unsigned long src_start,
1606 struct vm_area_struct **dst_vmap,
1607 struct vm_area_struct **src_vmap)
1608 {
1609 struct vm_area_struct *vma;
1610
1611 mmap_assert_locked(mm);
1612 vma = find_vma_and_prepare_anon(mm, dst_start);
1613 if (IS_ERR(vma))
1614 return PTR_ERR(vma);
1615
1616 *dst_vmap = vma;
1617 /* Skip finding src_vma if src_start is in dst_vma */
1618 if (src_start >= vma->vm_start && src_start < vma->vm_end)
1619 goto out_success;
1620
1621 vma = vma_lookup(mm, src_start);
1622 if (!vma)
1623 return -ENOENT;
1624 out_success:
1625 *src_vmap = vma;
1626 return 0;
1627 }
1628
1629 #ifdef CONFIG_PER_VMA_LOCK
uffd_move_lock(struct mm_struct * mm,unsigned long dst_start,unsigned long src_start,struct vm_area_struct ** dst_vmap,struct vm_area_struct ** src_vmap)1630 static int uffd_move_lock(struct mm_struct *mm,
1631 unsigned long dst_start,
1632 unsigned long src_start,
1633 struct vm_area_struct **dst_vmap,
1634 struct vm_area_struct **src_vmap)
1635 {
1636 struct vm_area_struct *vma;
1637 int err;
1638
1639 vma = uffd_lock_vma(mm, dst_start);
1640 if (IS_ERR(vma))
1641 return PTR_ERR(vma);
1642
1643 *dst_vmap = vma;
1644 /*
1645 * Skip finding src_vma if src_start is in dst_vma. This also ensures
1646 * that we don't lock the same vma twice.
1647 */
1648 if (src_start >= vma->vm_start && src_start < vma->vm_end) {
1649 *src_vmap = vma;
1650 return 0;
1651 }
1652
1653 /*
1654 * Using uffd_lock_vma() to get src_vma can lead to following deadlock:
1655 *
1656 * Thread1 Thread2
1657 * ------- -------
1658 * vma_start_read(dst_vma)
1659 * mmap_write_lock(mm)
1660 * vma_start_write(src_vma)
1661 * vma_start_read(src_vma)
1662 * mmap_read_lock(mm)
1663 * vma_start_write(dst_vma)
1664 */
1665 *src_vmap = lock_vma_under_rcu(mm, src_start);
1666 if (likely(*src_vmap))
1667 return 0;
1668
1669 /* Undo any locking and retry in mmap_lock critical section */
1670 vma_end_read(*dst_vmap);
1671
1672 mmap_read_lock(mm);
1673 err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
1674 if (err)
1675 goto out;
1676
1677 if (!vma_start_read_locked(*dst_vmap)) {
1678 err = -EAGAIN;
1679 goto out;
1680 }
1681
1682 /* Nothing further to do if both vmas are locked. */
1683 if (*dst_vmap == *src_vmap)
1684 goto out;
1685
1686 if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) {
1687 /* Undo dst_vmap locking if src_vmap failed to lock */
1688 vma_end_read(*dst_vmap);
1689 err = -EAGAIN;
1690 }
1691 out:
1692 mmap_read_unlock(mm);
1693 return err;
1694 }
1695
uffd_move_unlock(struct vm_area_struct * dst_vma,struct vm_area_struct * src_vma)1696 static void uffd_move_unlock(struct vm_area_struct *dst_vma,
1697 struct vm_area_struct *src_vma)
1698 {
1699 vma_end_read(src_vma);
1700 if (src_vma != dst_vma)
1701 vma_end_read(dst_vma);
1702 }
1703
1704 #else
1705
uffd_move_lock(struct mm_struct * mm,unsigned long dst_start,unsigned long src_start,struct vm_area_struct ** dst_vmap,struct vm_area_struct ** src_vmap)1706 static int uffd_move_lock(struct mm_struct *mm,
1707 unsigned long dst_start,
1708 unsigned long src_start,
1709 struct vm_area_struct **dst_vmap,
1710 struct vm_area_struct **src_vmap)
1711 {
1712 int err;
1713
1714 mmap_read_lock(mm);
1715 err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
1716 if (err)
1717 mmap_read_unlock(mm);
1718 return err;
1719 }
1720
uffd_move_unlock(struct vm_area_struct * dst_vma,struct vm_area_struct * src_vma)1721 static void uffd_move_unlock(struct vm_area_struct *dst_vma,
1722 struct vm_area_struct *src_vma)
1723 {
1724 mmap_assert_locked(src_vma->vm_mm);
1725 mmap_read_unlock(dst_vma->vm_mm);
1726 }
1727 #endif
1728
1729 /**
1730 * move_pages - move arbitrary anonymous pages of an existing vma
1731 * @ctx: pointer to the userfaultfd context
1732 * @dst_start: start of the destination virtual memory range
1733 * @src_start: start of the source virtual memory range
1734 * @len: length of the virtual memory range
1735 * @mode: flags from uffdio_move.mode
1736 *
1737 * It will either use the mmap_lock in read mode or per-vma locks
1738 *
1739 * move_pages() remaps arbitrary anonymous pages atomically in zero
1740 * copy. It only works on non shared anonymous pages because those can
1741 * be relocated without generating non linear anon_vmas in the rmap
1742 * code.
1743 *
1744 * It provides a zero copy mechanism to handle userspace page faults.
1745 * The source vma pages should have mapcount == 1, which can be
1746 * enforced by using madvise(MADV_DONTFORK) on src vma.
1747 *
1748 * The thread receiving the page during the userland page fault
1749 * will receive the faulting page in the source vma through the network,
1750 * storage or any other I/O device (MADV_DONTFORK in the source vma
1751 * avoids move_pages() to fail with -EBUSY if the process forks before
1752 * move_pages() is called), then it will call move_pages() to map the
1753 * page in the faulting address in the destination vma.
1754 *
1755 * This userfaultfd command works purely via pagetables, so it's the
1756 * most efficient way to move physical non shared anonymous pages
1757 * across different virtual addresses. Unlike mremap()/mmap()/munmap()
1758 * it does not create any new vmas. The mapping in the destination
1759 * address is atomic.
1760 *
1761 * It only works if the vma protection bits are identical from the
1762 * source and destination vma.
1763 *
1764 * It can remap non shared anonymous pages within the same vma too.
1765 *
1766 * If the source virtual memory range has any unmapped holes, or if
1767 * the destination virtual memory range is not a whole unmapped hole,
1768 * move_pages() will fail respectively with -ENOENT or -EEXIST. This
1769 * provides a very strict behavior to avoid any chance of memory
1770 * corruption going unnoticed if there are userland race conditions.
1771 * Only one thread should resolve the userland page fault at any given
1772 * time for any given faulting address. This means that if two threads
1773 * try to both call move_pages() on the same destination address at the
1774 * same time, the second thread will get an explicit error from this
1775 * command.
1776 *
1777 * The command retval will return "len" is successful. The command
1778 * however can be interrupted by fatal signals or errors. If
1779 * interrupted it will return the number of bytes successfully
1780 * remapped before the interruption if any, or the negative error if
1781 * none. It will never return zero. Either it will return an error or
1782 * an amount of bytes successfully moved. If the retval reports a
1783 * "short" remap, the move_pages() command should be repeated by
1784 * userland with src+retval, dst+reval, len-retval if it wants to know
1785 * about the error that interrupted it.
1786 *
1787 * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to
1788 * prevent -ENOENT errors to materialize if there are holes in the
1789 * source virtual range that is being remapped. The holes will be
1790 * accounted as successfully remapped in the retval of the
1791 * command. This is mostly useful to remap hugepage naturally aligned
1792 * virtual regions without knowing if there are transparent hugepage
1793 * in the regions or not, but preventing the risk of having to split
1794 * the hugepmd during the remap.
1795 *
1796 * If there's any rmap walk that is taking the anon_vma locks without
1797 * first obtaining the folio lock (the only current instance is
1798 * folio_referenced), they will have to verify if the folio->mapping
1799 * has changed after taking the anon_vma lock. If it changed they
1800 * should release the lock and retry obtaining a new anon_vma, because
1801 * it means the anon_vma was changed by move_pages() before the lock
1802 * could be obtained. This is the only additional complexity added to
1803 * the rmap code to provide this anonymous page remapping functionality.
1804 */
move_pages(struct userfaultfd_ctx * ctx,unsigned long dst_start,unsigned long src_start,unsigned long len,__u64 mode)1805 ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
1806 unsigned long src_start, unsigned long len, __u64 mode)
1807 {
1808 struct mm_struct *mm = ctx->mm;
1809 struct vm_area_struct *src_vma, *dst_vma;
1810 unsigned long src_addr, dst_addr, src_end;
1811 pmd_t *src_pmd, *dst_pmd;
1812 long err = -EINVAL;
1813 ssize_t moved = 0;
1814
1815 /* Sanitize the command parameters. */
1816 VM_WARN_ON_ONCE(src_start & ~PAGE_MASK);
1817 VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
1818 VM_WARN_ON_ONCE(len & ~PAGE_MASK);
1819
1820 /* Does the address range wrap, or is the span zero-sized? */
1821 VM_WARN_ON_ONCE(src_start + len < src_start);
1822 VM_WARN_ON_ONCE(dst_start + len < dst_start);
1823
1824 err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
1825 if (err)
1826 goto out;
1827
1828 /* Re-check after taking map_changing_lock */
1829 err = -EAGAIN;
1830 down_read(&ctx->map_changing_lock);
1831 if (likely(atomic_read(&ctx->mmap_changing)))
1832 goto out_unlock;
1833 /*
1834 * Make sure the vma is not shared, that the src and dst remap
1835 * ranges are both valid and fully within a single existing
1836 * vma.
1837 */
1838 err = -EINVAL;
1839 if (src_vma->vm_flags & VM_SHARED)
1840 goto out_unlock;
1841 if (src_start + len > src_vma->vm_end)
1842 goto out_unlock;
1843
1844 if (dst_vma->vm_flags & VM_SHARED)
1845 goto out_unlock;
1846 if (dst_start + len > dst_vma->vm_end)
1847 goto out_unlock;
1848
1849 err = validate_move_areas(ctx, src_vma, dst_vma);
1850 if (err)
1851 goto out_unlock;
1852
1853 for (src_addr = src_start, dst_addr = dst_start, src_end = src_start + len;
1854 src_addr < src_end;) {
1855 spinlock_t *ptl;
1856 pmd_t dst_pmdval;
1857 unsigned long step_size;
1858
1859 /*
1860 * Below works because anonymous area would not have a
1861 * transparent huge PUD. If file-backed support is added,
1862 * that case would need to be handled here.
1863 */
1864 src_pmd = mm_find_pmd(mm, src_addr);
1865 if (unlikely(!src_pmd)) {
1866 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
1867 err = -ENOENT;
1868 break;
1869 }
1870 src_pmd = mm_alloc_pmd(mm, src_addr);
1871 if (unlikely(!src_pmd)) {
1872 err = -ENOMEM;
1873 break;
1874 }
1875 }
1876 dst_pmd = mm_alloc_pmd(mm, dst_addr);
1877 if (unlikely(!dst_pmd)) {
1878 err = -ENOMEM;
1879 break;
1880 }
1881
1882 dst_pmdval = pmdp_get_lockless(dst_pmd);
1883 /*
1884 * If the dst_pmd is mapped as THP don't override it and just
1885 * be strict. If dst_pmd changes into TPH after this check, the
1886 * move_pages_huge_pmd() will detect the change and retry
1887 * while move_pages_pte() will detect the change and fail.
1888 */
1889 if (unlikely(pmd_trans_huge(dst_pmdval))) {
1890 err = -EEXIST;
1891 break;
1892 }
1893
1894 ptl = pmd_trans_huge_lock(src_pmd, src_vma);
1895 if (ptl) {
1896 /* Check if we can move the pmd without splitting it. */
1897 if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
1898 !pmd_none(dst_pmdval)) {
1899 /* Can be a migration entry */
1900 if (pmd_present(*src_pmd)) {
1901 struct folio *folio = pmd_folio(*src_pmd);
1902
1903 if (!is_huge_zero_folio(folio) &&
1904 !PageAnonExclusive(&folio->page)) {
1905 spin_unlock(ptl);
1906 err = -EBUSY;
1907 break;
1908 }
1909 }
1910
1911 spin_unlock(ptl);
1912 split_huge_pmd(src_vma, src_pmd, src_addr);
1913 /* The folio will be split by move_pages_pte() */
1914 continue;
1915 }
1916
1917 err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
1918 dst_pmdval, dst_vma, src_vma,
1919 dst_addr, src_addr);
1920 step_size = HPAGE_PMD_SIZE;
1921 } else {
1922 long ret;
1923
1924 if (pmd_none(*src_pmd)) {
1925 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
1926 err = -ENOENT;
1927 break;
1928 }
1929 if (unlikely(__pte_alloc(mm, src_pmd))) {
1930 err = -ENOMEM;
1931 break;
1932 }
1933 }
1934
1935 if (unlikely(pte_alloc(mm, dst_pmd))) {
1936 err = -ENOMEM;
1937 break;
1938 }
1939
1940 ret = move_pages_ptes(mm, dst_pmd, src_pmd,
1941 dst_vma, src_vma, dst_addr,
1942 src_addr, src_end - src_addr, mode);
1943 if (ret < 0)
1944 err = ret;
1945 else
1946 step_size = ret;
1947 }
1948
1949 cond_resched();
1950
1951 if (fatal_signal_pending(current)) {
1952 /* Do not override an error */
1953 if (!err || err == -EAGAIN)
1954 err = -EINTR;
1955 break;
1956 }
1957
1958 if (err) {
1959 if (err == -EAGAIN)
1960 continue;
1961 break;
1962 }
1963
1964 /* Proceed to the next page */
1965 dst_addr += step_size;
1966 src_addr += step_size;
1967 moved += step_size;
1968 }
1969
1970 out_unlock:
1971 up_read(&ctx->map_changing_lock);
1972 uffd_move_unlock(dst_vma, src_vma);
1973 out:
1974 VM_WARN_ON_ONCE(moved < 0);
1975 VM_WARN_ON_ONCE(err > 0);
1976 VM_WARN_ON_ONCE(!moved && !err);
1977 return moved ? moved : err;
1978 }
1979
userfaultfd_set_vm_flags(struct vm_area_struct * vma,vm_flags_t vm_flags)1980 static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
1981 vm_flags_t vm_flags)
1982 {
1983 const bool uffd_wp_changed = (vma->vm_flags ^ vm_flags) & VM_UFFD_WP;
1984
1985 vm_flags_reset(vma, vm_flags);
1986 /*
1987 * For shared mappings, we want to enable writenotify while
1988 * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
1989 * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
1990 */
1991 if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
1992 vma_set_page_prot(vma);
1993 }
1994
userfaultfd_set_ctx(struct vm_area_struct * vma,struct userfaultfd_ctx * ctx,vm_flags_t vm_flags)1995 static void userfaultfd_set_ctx(struct vm_area_struct *vma,
1996 struct userfaultfd_ctx *ctx,
1997 vm_flags_t vm_flags)
1998 {
1999 vma_start_write(vma);
2000 vma->vm_userfaultfd_ctx = (struct vm_userfaultfd_ctx){ctx};
2001 userfaultfd_set_vm_flags(vma,
2002 (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags);
2003 }
2004
userfaultfd_reset_ctx(struct vm_area_struct * vma)2005 void userfaultfd_reset_ctx(struct vm_area_struct *vma)
2006 {
2007 userfaultfd_set_ctx(vma, NULL, 0);
2008 }
2009
userfaultfd_clear_vma(struct vma_iterator * vmi,struct vm_area_struct * prev,struct vm_area_struct * vma,unsigned long start,unsigned long end)2010 struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
2011 struct vm_area_struct *prev,
2012 struct vm_area_struct *vma,
2013 unsigned long start,
2014 unsigned long end)
2015 {
2016 struct vm_area_struct *ret;
2017 bool give_up_on_oom = false;
2018
2019 /*
2020 * If we are modifying only and not splitting, just give up on the merge
2021 * if OOM prevents us from merging successfully.
2022 */
2023 if (start == vma->vm_start && end == vma->vm_end)
2024 give_up_on_oom = true;
2025
2026 /* Reset ptes for the whole vma range if wr-protected */
2027 if (userfaultfd_wp(vma))
2028 uffd_wp_range(vma, start, end - start, false);
2029
2030 ret = vma_modify_flags_uffd(vmi, prev, vma, start, end,
2031 vma->vm_flags & ~__VM_UFFD_FLAGS,
2032 NULL_VM_UFFD_CTX, give_up_on_oom);
2033
2034 /*
2035 * In the vma_merge() successful mprotect-like case 8:
2036 * the next vma was merged into the current one and
2037 * the current one has not been updated yet.
2038 */
2039 if (!IS_ERR(ret))
2040 userfaultfd_reset_ctx(ret);
2041
2042 return ret;
2043 }
2044
2045 /* Assumes mmap write lock taken, and mm_struct pinned. */
userfaultfd_register_range(struct userfaultfd_ctx * ctx,struct vm_area_struct * vma,vm_flags_t vm_flags,unsigned long start,unsigned long end,bool wp_async)2046 int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
2047 struct vm_area_struct *vma,
2048 vm_flags_t vm_flags,
2049 unsigned long start, unsigned long end,
2050 bool wp_async)
2051 {
2052 VMA_ITERATOR(vmi, ctx->mm, start);
2053 struct vm_area_struct *prev = vma_prev(&vmi);
2054 unsigned long vma_end;
2055 vm_flags_t new_flags;
2056
2057 if (vma->vm_start < start)
2058 prev = vma;
2059
2060 for_each_vma_range(vmi, vma, end) {
2061 cond_resched();
2062
2063 VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async));
2064 VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx &&
2065 vma->vm_userfaultfd_ctx.ctx != ctx);
2066 VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
2067
2068 /*
2069 * Nothing to do: this vma is already registered into this
2070 * userfaultfd and with the right tracking mode too.
2071 */
2072 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
2073 (vma->vm_flags & vm_flags) == vm_flags)
2074 goto skip;
2075
2076 if (vma->vm_start > start)
2077 start = vma->vm_start;
2078 vma_end = min(end, vma->vm_end);
2079
2080 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
2081 vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
2082 new_flags,
2083 (struct vm_userfaultfd_ctx){ctx},
2084 /* give_up_on_oom = */false);
2085 if (IS_ERR(vma))
2086 return PTR_ERR(vma);
2087
2088 /*
2089 * In the vma_merge() successful mprotect-like case 8:
2090 * the next vma was merged into the current one and
2091 * the current one has not been updated yet.
2092 */
2093 userfaultfd_set_ctx(vma, ctx, vm_flags);
2094
2095 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
2096 hugetlb_unshare_all_pmds(vma);
2097
2098 skip:
2099 prev = vma;
2100 start = vma->vm_end;
2101 }
2102
2103 return 0;
2104 }
2105
userfaultfd_release_new(struct userfaultfd_ctx * ctx)2106 void userfaultfd_release_new(struct userfaultfd_ctx *ctx)
2107 {
2108 struct mm_struct *mm = ctx->mm;
2109 struct vm_area_struct *vma;
2110 VMA_ITERATOR(vmi, mm, 0);
2111
2112 /* the various vma->vm_userfaultfd_ctx still points to it */
2113 mmap_write_lock(mm);
2114 for_each_vma(vmi, vma) {
2115 if (vma->vm_userfaultfd_ctx.ctx == ctx)
2116 userfaultfd_reset_ctx(vma);
2117 }
2118 mmap_write_unlock(mm);
2119 }
2120
userfaultfd_release_all(struct mm_struct * mm,struct userfaultfd_ctx * ctx)2121 void userfaultfd_release_all(struct mm_struct *mm,
2122 struct userfaultfd_ctx *ctx)
2123 {
2124 struct vm_area_struct *vma, *prev;
2125 VMA_ITERATOR(vmi, mm, 0);
2126
2127 if (!mmget_not_zero(mm))
2128 return;
2129
2130 /*
2131 * Flush page faults out of all CPUs. NOTE: all page faults
2132 * must be retried without returning VM_FAULT_SIGBUS if
2133 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
2134 * changes while handle_userfault released the mmap_lock. So
2135 * it's critical that released is set to true (above), before
2136 * taking the mmap_lock for writing.
2137 */
2138 mmap_write_lock(mm);
2139 prev = NULL;
2140 for_each_vma(vmi, vma) {
2141 cond_resched();
2142 VM_WARN_ON_ONCE(!!vma->vm_userfaultfd_ctx.ctx ^
2143 !!(vma->vm_flags & __VM_UFFD_FLAGS));
2144 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
2145 prev = vma;
2146 continue;
2147 }
2148
2149 vma = userfaultfd_clear_vma(&vmi, prev, vma,
2150 vma->vm_start, vma->vm_end);
2151 prev = vma;
2152 }
2153 mmap_write_unlock(mm);
2154 mmput(mm);
2155 }
2156